#!/usr/bin/env python
"""This server runs an XMLRPC server that can be submitted code and tests
and returns the output.  It *should* be run as root and will run as the user 
'nobody' so as to minimize any damange by errant code.
"""
import sys
import traceback
from SimpleXMLRPCServer import SimpleXMLRPCServer
import pwd
import os
from os.path import isdir


# Set the effective uid
nobody = pwd.getpwnam('nobody')
os.setegid(nobody.pw_gid)
os.seteuid(nobody.pw_uid)


def run_code(answer, test_code, in_dir=None):
    """Tests given Python function (`answer`) with the `test_code` supplied.  
    If the optional `in_dir` keyword argument is supplied it changes the 
    directory to that directory (it does not change it back to the original when
    done).

    Returns
    -------
    
    A tuple: (success, error message).
    
    """
    if in_dir is not None and isdir(in_dir):
        os.chdir(in_dir)
        
    success = False
    tb = None
    try:
        submitted = compile(answer, '<string>', mode='exec')
        g = {}
        exec submitted in g
        _tests = compile(test_code, '<string>', mode='exec')
        exec _tests in g
    except AssertionError:
        type, value, tb = sys.exc_info()
        info = traceback.extract_tb(tb)
        fname, lineno, func, text = info[-1]
        text = str(test_code).splitlines()[lineno-1]
        err = "{0} {1} in: {2}".format(type.__name__, str(value), text)
    except:
        type, value = sys.exc_info()[:2]
        err = "Error: {0}".format(repr(value))
    else:
        success = True
        err = 'Correct answer'
    finally:
        del tb

    return success, err


def main():
    server = SimpleXMLRPCServer(("localhost", 8001))
    server.register_function(run_code)
    server.serve_forever()
    
if __name__ == '__main__':
    main()